Francoise C. Clarke

Isolation and characterization of an anticoagulant present in the salivary glands of the bont-legged tick, Hyalomma truncatum

A low molecular mass anticoagulant (17 kDa) was isolated from the salivary glands of prefed female Hyalomma truncatum ticks by means of reverse phase and anion-exchange HPLC. Trypsin digestion and amino acid analysis confirmed the protein nature of the anticoagulant. The inhibitor appears to be uncompetitive with a Ki of 6.9×10−10M. The target of the anticoagulant is factor Xa at the junction of the extrinsic and intrinsic pathways. This may be crucial for the survival of the tick, making it feasible to investigate the possibility of vaccination with this antihaemostatic against tick feeding. In addition, tick anticoagulants may possibly have therapeutic application in controlling thrombosis.

Geometric morphometric analyses of the male and female body shape of Hyalomma truncatum and H. Marginatum rufipes (Acari: Ixodidae)

Abstract A geometric morphometric analysis of the male and female body shape of two species belonging to the Ixodidae, Hyalomma truncatum (Koch) and H. marginatum rufipes (Koch) was performed. These two species are very similar in adult appearance, and only the well-trained researcher is able to distinguish between them. This analysis compares the body shape of the ticks with each other by collecting 16 landmarks from the males and females and analyzing this with a powerful statistical technique, geometric morphometrics. Relative warp analyses were performed on the data set and the results of the first two relative warps (for each of the male and female data set) plotted against one another. The first two relative warps are indicative of the most variation between structures that are studied. Thin-plate-spline analyses were also performed on the consensus shape of the males and females. Results from thin-plate spline analysis visually provide input regarding landmarks that are responsible for shape similarities and differences. Geometric morphometrics is a powerful tool that can be used successfully to identify phenetic relationships between taxa, and could be an additional tool to be used by tick systematists.

Development of resistance in laboratory animals to adults of the tick Rhipicephalus evertsi evertsi.

Abstract. Acquired resistance to adults of the two‐host tick Rhipicephalus evertsi evertsi Neumann has been demonstrated in guinea‐pigs and rabbits. Four infestations of both hosts with R.e.evertsi adults resulted in a significant reduction in the mean weight of the engorged females. A decline in the mean weight of the female ticks was also observed in ticks which fed on a rabbit previously injected with serum taken from a rabbit resistant to R.e.evertsi. This suggests that humoral immunity may have an important role in the acquired resistance to ticks. In both hosts an increase in the level of serum globulins was recorded. In rabbits the level of gamma globulin was affected, while in guinea‐pigs an increase was observed in the concentration of α and β globulins. The differences in host responses to the R.e.evertsi adults are discussed.

Geometric morphometric analysis of the male and female body shape of Amblyomma gemma, A. variegatum and A. hebraeum

Abstract A geometric morphometric analysis of the male and female body shape of three species belonging to the Ixodidae, Amblyomma gemma Dönitz, A. variegatum (Fab.) and A. hebraeum Koch, was performed. These three species are very similar in adult appearance and their distributions overlaps, covering virtually all of sub-Saharan Africa. This analysis compares the body shape of the ticks with each other by collecting 17 landmarks from the ventral area of males and females and analyzing these with geometric morphometrics. Relative warp analyses were performed on the male and female data sets and the results of the first two relative warps (for each of the male and female data sets) were plotted against one another. The first two relative warps are indicative of most variation between structures that were studied. Thin-plate spline analyses were also performed on the consensus shape of the males and females. Results from thin-plate spline analysis indicate which landmarks are responsible for shape variations. Results from the analysis indicate that the body shapes of A. gemma and A. variegatum females cannot be distinguished from each other. The male body shape of the two species is also very similar, as indicated by the consensus thin-plate splines.

A comparison of geometric morphometic analyses and cross-breeding as methods to determine relatedness in three Amblyomma species (Acari: Ixodidae)

Abstract Amblyomma gemma (Dönitz, 1909), A. hebraeum (Koch, 1844) and A. variegatum (Fabricius, 1794) and A. are generally accepted as distinct species. The three species, however, correspond in many aspects, overlapping in distribution, altitude and rainfall tolerances, occurring in the same habitat type, preferring the same hosts and using the same predilection sites. Amblyomma variegatum differs from the other two species in appearance. There is, however, a close resemblance in the scutal pattern of the males of the other two species and the females of A. gemma and A hebraeum are almost indistinguishable. The degree of similarities between the three species was therefore investigated through morphological comparison, geometric morphometric analyses and attempts to cross breed. The geometric morphometric analyses based on ventral body shape of the malesand females of the three species indicate that A. variegatum and A. gemma are similar, suggesting that the two ticks might not be distinct species as is presently recognized. The geometric morphometric analyses indicate that A. hebraeum differs in ventral body shape from the other species and that the ventral body shape of the A. gemma - A. hebraeum cross Fl adults shows a greater resemblance to that of A. gemma than to that of A. hebraeum. This is contrary to the outcome of the crossbreeding experiments that suggests that A. variegatum is not genetically compatible to either of the other two species but that the species A. gemma and A. hebraeum are genetically compatible.

Assessment of acquired immune response to Rhipicephalus appendiculatus tick infestation in different goat breeds

Changes in serum gamma globulin levels, numbers of replete female ticks and engorged tick mass were used as parameters to monitor the acquired immune response (antibody mediated immune response) elicited by Rhipicephalus appendiculatus adult tick infestations. Three consecutive Rhipicephalus appendiculatus adult tick infestations were applied to South African Indigenous goats (Nguni), Saanen goats and cross-bred goats (Saanen goats crossed with South African Indigenous goats [Nguni]) under laboratory conditions. During the three consecutive Rhipicephalus appendiculatus adult tick infestations the serum gamma globulin levels increased in all three breeds, whilst the mean replete female tick numbers and engorged tick mass decreased. Even though all three goat breeds exhibited an acquired immune response, the South African Indigenous goats (Nguni) response was significantly higher than that of the Saanen and cross-bred goats. However, the acquired immune response elicited by Saanen goats was significantly lower when compared with cross-bred goats.

Gynandromorphism in Hyalomma Truncatum (Acarl:Ixodidae)

This short communication describes the morphological features of three specimens of Hyalomma truncatum which dropped off artificially infested rabbits in the laboratory.RésuméCette présentation succinte décrit les caractéres morphologiques differentiels de 3 specimens de Hyalomma truncatum collectés de lapins aprés une infestation artificielle au laboratoire.